// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include <stddef.h>

#include <algorithm>

#include "base/logging.h"
#include "base/macros.h"
#include "media/filters/h264_parser.h"
#include "media/video/h264_poc.h"

namespace media {

H264POC::H264POC()
{
    Reset();
}

H264POC::~H264POC()
{
}

void H264POC::Reset()
{
    // It shouldn't be necessary to reset these values, but doing so will improve
    // reproducibility for buggy streams.
    ref_pic_order_cnt_msb_ = 0;
    ref_pic_order_cnt_lsb_ = 0;
    prev_frame_num_ = 0;
    prev_frame_num_offset_ = 0;
}

// Check if a slice includes memory management control operation 5, which
// results in some |pic_order_cnt| state being cleared.
static bool HasMMCO5(const media::H264SliceHeader& slice_hdr)
{
    // Require that the frame actually has memory management control operations.
    if (slice_hdr.nal_ref_idc == 0 || slice_hdr.idr_pic_flag || !slice_hdr.adaptive_ref_pic_marking_mode_flag) {
        return false;
    }

    for (size_t i = 0; i < arraysize(slice_hdr.ref_pic_marking); i++) {
        int32_t op = slice_hdr.ref_pic_marking[i].memory_mgmnt_control_operation;
        if (op == 5)
            return true;

        // Stop at the end of the list.
        if (op == 0)
            return false;
    }

    // Should not get here, the list is always zero terminated.
    return false;
}

bool H264POC::ComputePicOrderCnt(
    const H264SPS* sps,
    const H264SliceHeader& slice_hdr,
    int32_t* pic_order_cnt)
{
    if (slice_hdr.field_pic_flag) {
        DLOG(ERROR) << "Interlaced frames are not supported";
        return false;
    }

    bool mmco5 = HasMMCO5(slice_hdr);
    int32_t max_frame_num = 1 << (sps->log2_max_frame_num_minus4 + 4);
    int32_t max_pic_order_cnt_lsb = 1 << (sps->log2_max_pic_order_cnt_lsb_minus4 + 4);

    // Note: Duplicate frame numbers are ignored. They occur in many videos
    // despite appearing to be invalid according to the spec.
    // TODO(sandersd): Check if these videos are using slices or have redundant
    // streams.

    // Note: Gaps in frame numbers are also ignored. They do not affect POC
    // computation.

    // Based on T-REC-H.264 8.2.1, "Decoding process for picture order
    // count", available from http://www.itu.int/rec/T-REC-H.264.
    //
    // Reorganized slightly from spec pseudocode to handle MMCO5 when storing
    // state instead of when loading it.
    switch (sps->pic_order_cnt_type) {
    case 0: {
        int32_t prev_pic_order_cnt_msb = ref_pic_order_cnt_msb_;
        int32_t prev_pic_order_cnt_lsb = ref_pic_order_cnt_lsb_;

        // For an IDR picture, clear the state.
        if (slice_hdr.idr_pic_flag) {
            prev_pic_order_cnt_msb = 0;
            prev_pic_order_cnt_lsb = 0;
        }

        // 8-3. Derive |pic_order_cnt_msb|, accounting for wrapping which is
        //      detected when |pic_order_cnt_lsb| increases or decreases by at
        //      least half of its maximum.
        int32_t pic_order_cnt_msb;
        if ((slice_hdr.pic_order_cnt_lsb < prev_pic_order_cnt_lsb) && (prev_pic_order_cnt_lsb - slice_hdr.pic_order_cnt_lsb >= max_pic_order_cnt_lsb / 2)) {
            pic_order_cnt_msb = prev_pic_order_cnt_msb + max_pic_order_cnt_lsb;
        } else if ((slice_hdr.pic_order_cnt_lsb > prev_pic_order_cnt_lsb) && (slice_hdr.pic_order_cnt_lsb - prev_pic_order_cnt_lsb > max_pic_order_cnt_lsb / 2)) {
            pic_order_cnt_msb = prev_pic_order_cnt_msb - max_pic_order_cnt_lsb;
        } else {
            pic_order_cnt_msb = prev_pic_order_cnt_msb;
        }

        // 8-4, 8-5. Derive |top_field_order_count| and |bottom_field_order_cnt|
        //           (assuming no interlacing).
        int32_t top_foc = pic_order_cnt_msb + slice_hdr.pic_order_cnt_lsb;
        int32_t bottom_foc = top_foc + slice_hdr.delta_pic_order_cnt_bottom;
        *pic_order_cnt = std::min(top_foc, bottom_foc);

        // Store state.
        prev_frame_num_ = slice_hdr.frame_num;
        if (slice_hdr.nal_ref_idc != 0) {
            if (mmco5) {
                ref_pic_order_cnt_msb_ = 0;
                ref_pic_order_cnt_lsb_ = top_foc;
            } else {
                ref_pic_order_cnt_msb_ = pic_order_cnt_msb;
                ref_pic_order_cnt_lsb_ = slice_hdr.pic_order_cnt_lsb;
            }
        }

        break;
    }

    case 1: {
        // 8-6. Derive |frame_num_offset|.
        int32_t frame_num_offset;
        if (slice_hdr.idr_pic_flag)
            frame_num_offset = 0;
        else if (prev_frame_num_ > slice_hdr.frame_num)
            frame_num_offset = prev_frame_num_offset_ + max_frame_num;
        else
            frame_num_offset = prev_frame_num_offset_;

        // 8-7. Derive |abs_frame_num|.
        int32_t abs_frame_num;
        if (sps->num_ref_frames_in_pic_order_cnt_cycle != 0)
            abs_frame_num = frame_num_offset + slice_hdr.frame_num;
        else
            abs_frame_num = 0;

        if (slice_hdr.nal_ref_idc == 0 && abs_frame_num > 0)
            abs_frame_num--;

        // 8-9. Derive |expected_pic_order_cnt| (the |pic_order_cnt| indicated
        //      by the cycle described in the SPS).
        int32_t expected_pic_order_cnt = 0;
        if (abs_frame_num > 0) {
            // 8-8. Derive pic_order_cnt_cycle_cnt and
            //      frame_num_in_pic_order_cnt_cycle.
            // Moved inside 8-9 to avoid division when this check is not done.
            if (sps->num_ref_frames_in_pic_order_cnt_cycle == 0) {
                DLOG(ERROR) << "Invalid num_ref_frames_in_pic_order_cnt_cycle";
                return false;
            }

            // H264Parser checks that num_ref_frames_in_pic_order_cnt_cycle < 255.
            int32_t pic_order_cnt_cycle_cnt = (abs_frame_num - 1) / sps->num_ref_frames_in_pic_order_cnt_cycle;
            int32_t frame_num_in_pic_order_cnt_cycle = (abs_frame_num - 1) % sps->num_ref_frames_in_pic_order_cnt_cycle;

            // 8-9 continued.
            expected_pic_order_cnt = pic_order_cnt_cycle_cnt * sps->expected_delta_per_pic_order_cnt_cycle;
            for (int32_t i = 0; i <= frame_num_in_pic_order_cnt_cycle; i++)
                expected_pic_order_cnt += sps->offset_for_ref_frame[i];
        }
        if (slice_hdr.nal_ref_idc == 0)
            expected_pic_order_cnt += sps->offset_for_non_ref_pic;

        // 8-10. Derive |top_field_order_cnt| and |bottom_field_order_cnt|
        //       (assuming no interlacing).
        int32_t top_foc = expected_pic_order_cnt + slice_hdr.delta_pic_order_cnt0;
        int32_t bottom_foc = top_foc + sps->offset_for_top_to_bottom_field + slice_hdr.delta_pic_order_cnt1;
        *pic_order_cnt = std::min(top_foc, bottom_foc);

        // Store state.
        prev_frame_num_ = slice_hdr.frame_num;
        prev_frame_num_offset_ = frame_num_offset;
        if (mmco5)
            prev_frame_num_offset_ = 0;

        break;
    }

    case 2: {
        // 8-11. Derive |frame_num_offset|.
        int32_t frame_num_offset;
        if (slice_hdr.idr_pic_flag)
            frame_num_offset = 0;
        else if (prev_frame_num_ > slice_hdr.frame_num)
            frame_num_offset = prev_frame_num_offset_ + max_frame_num;
        else
            frame_num_offset = prev_frame_num_offset_;

        // 8-12, 8-13. Derive |temp_pic_order_count| (it's always the
        // |pic_order_cnt|, regardless of interlacing).
        if (slice_hdr.idr_pic_flag)
            *pic_order_cnt = 0;
        else if (slice_hdr.nal_ref_idc == 0)
            *pic_order_cnt = 2 * (frame_num_offset + slice_hdr.frame_num) - 1;
        else
            *pic_order_cnt = 2 * (frame_num_offset + slice_hdr.frame_num);

        // Store state.
        prev_frame_num_ = slice_hdr.frame_num;
        prev_frame_num_offset_ = frame_num_offset;
        if (mmco5)
            prev_frame_num_offset_ = 0;

        break;
    }

    default:
        DLOG(ERROR) << "Invalid pic_order_cnt_type: " << sps->pic_order_cnt_type;
        return false;
    }

    return true;
}

} // namespace media
